Enhancement of adsorption via polarization in a composite material

ABSTRACT

A composite adsorbent material includes a component that creates a localized electric field and a porous material where adsorption occurs, wherein the localized electric field extends into the porous material. The localized electric field created by the component controls adsorption properties of the porous material. The porous material may be microporous. The component may include ferroelectric material including a β-phase of polyvinylidene fluoride (PVDF), and wherein the porous material may include any of zeolites, silicas, activated carbons, covalent organic frameworks (COFs), polymers of intrinsic microporosity (PIMs), and metal-organic frameworks (MOFs). The MOFs may include any of HKUST-1, UiO-66, and UiO-66-NH2. The β-phase of PVDF and the HKUST-1 may be electrospun together. The β-phase of PVDF includes aligned polymer chains that create the localized electric field extending within the porous material. The localized electric field enhances adsorption of an adsorbate, particularly a non-polar adsorbate such as oxygen or carbon dioxide, to the porous material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/385,300filed on Dec. 20, 2016, now U.S. Pat. No. 10,427,134 which is commonlyassigned.

GOVERNMENT INTEREST

The embodiments herein may be manufactured, used, and/or licensed by orfor the United States Government without the payment of royaltiesthereon.

BACKGROUND Technical Field

The embodiments herein generally relate to adsorption techniques, andmore particularly to adsorption in composite materials.

Description of the Related Art

Generally, adsorption involves the attraction of molecules (adsorbate)to a surface (adsorbent). Adsorption has been known to be governed bythree main factors: (1) the concentration of active adsorbent sites; (2)the strength of the adsorbent-adsorbate interaction; and (3) thestrength of interactions between independent adsorbate molecules.However, without an external force on the surface material, adsorptionis limited by these factors. For polar adsorbates, or those that canform chemical bonds with the adsorbent, adsorption can, in many cases,be quite great, even at low pressures; however, for non-polar gases,such as oxygen, carbon dioxide, or methane, adsorption is typicallyquite limited as there is minimal attraction between the adsorbent andadsorbate.

SUMMARY

In view of the foregoing, an embodiment herein provides a compositematerial comprising a component that creates a localized electric field;and a porous material where adsorption occurs, wherein the localizedelectric field extends into the porous material. The localized electricfield created by the component controls adsorption properties of theporous material. The porous material may be microporous. The componentmay comprise ferroelectric material comprising a β-phase ofpolyvinylidene fluoride (PVDF), wherein the porous material may compriseany of zeolites, silicas, activated carbons, covalent organic frameworks(COFs), polymers of intrinsic microporosity (PIMs), and metal-organicframeworks (MOFs). The MOFs may comprise any of HKUST-1, UiO-66, andUiO-66-NH₂. The β-phase of PVDF and the HKUST-1 may be electrospuntogether. The β-phase of PVDF comprises aligned polymer chains, whereinthe aligned polymer chains create the localized electric field extendingwithin the porous material. The localized electric field may enhance anadsorption of an adsorbate to the porous material. The localizedelectric field may enhance an adsorption of a non-polar adsorbate to theporous material. The localized electric field may enhance an adsorptionof oxygen to the porous material.

Another embodiment provides a method of adsorption comprising providinga composite material comprising a component that creates a localizedelectric field throughout the composite material; and a porous materialwhere adsorption occurs, wherein the localized electric field extendsinto the porous material; and providing an adsorbate for adsorption bythe composite material, wherein the localized electric field created bythe component controls adsorption properties of the porous material. Theporous material may be microporous. The component may compriseferroelectric material comprising a β-phase of PVDF. The porous materialmay comprise any of zeolites, silicas activated carbons, COFs, PIMs, andMOFs. The MOFs may comprise any of HKUST-1, UiO-66, and UiO-66-NH₂. Themethod may further comprise electrospinning the β-phase of PVDF and theHKUST-1 together. The β-phase of PVDF comprises aligned polymer chains,wherein the aligned polymer chains create the localized electric fieldextending within the porous material. The localized electric field mayenhance an adsorption of an adsorbate to the porous material. Thelocalized electric field may enhance an adsorption of a non-polaradsorbate to the porous material. The localized electric field mayenhance an adsorption of oxygen to the porous material.

These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments and numerous specific details thereof, are givenby way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments hereinwithout departing from the spirit thereof, and the embodiments hereininclude all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1 is a cross-sectional side view of a ferroelectric-adsorbentcomposite with an aligned electric field according to the embodimentsherein;

FIG. 2A is a graphical representation illustrating oxygen uptakeisotherms for various HKUST-1-PVDF composites according to theembodiments herein;

FIG. 2B is a graphical representation illustrating oxygen uptakeisotherms for various HKUST-1-PVDF composites scaled for adsorbentcontent according to the embodiments herein;

FIG. 3 is a schematic diagram illustrating theα-(trans-gauche-trans-gauche), β-(trans-trans-trans-trans), andγ-(trans-trans-trans-gauche) phases of PVDF according to the embodimentsherein;

FIG. 4A is a scanning electron micrograph (SEM) image of PVDF-MOFelectrospun phases according to the embodiments herein;

FIG. 4B is a schematic diagram illustrating a PVDF-MOF nanofiber showingthe alignment of individual polymer molecules according to theembodiments herein;

FIG. 4C is a schematic diagram illustrating the alignment of the dipolesto the adsorbate (oxygen) with the polymer fibers to enhance theadsorption according to the embodiments herein; and

FIG. 5 is a flow diagram illustrating a method according to anembodiment herein.

DETAILED DESCRIPTION

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

The embodiments herein provide a technique to utilize the ferroelectriccapability of one material in a composite to increase the uptake of anadsorbate of interest by a porous material in the composite. Referringnow to the drawings, and more particularly to FIGS. 1 through 5, wheresimilar reference characters denote corresponding features consistentlythroughout the figures, there are shown preferred embodiments.

FIG. 1 illustrates a composite material 5 comprising a component 10 thatcreates a localized electric field 20 throughout the composite material5; and a porous material 15 where adsorption of an adsorbate (e.g.,molecule) 25 occurs, wherein the localized electric field 20 extendsinto the porous material 15. In general, the composite material 5 hastwo characteristics that may either come from one or multiple components10, 15: (1) the material 5 exhibits a localized electric field 20arising from a component 10 such as ferroelectric material comprisingβ-phase of polyvinylidene fluoride (PVDF); and (2) the electric field 20extends into the porous material 15 where adsorption occurs. In theexample shown in FIG. 1, the electric field 20 is locally aligned by thecomponent 10. The electric field 20, in turn, affects the sorptionproperties of the adsorbent (e.g., porous material 15).

Sorbents with micropores (i.e., pores less than two nanometers indiameter), such as zeolites, activated carbons, and metal-organicframeworks (MOFs), are quite effective for adsorption of smallmolecules. For instance, the MOF known as HKUST-1 (Hong Kong Universityof Science and Technology) is particularly effective at the sorption ofoxygen. When a composite of HKUST-1 and PVDF are electrospun together ina composite material 5, there is a nearly ten-fold increase in thesorption capacity of the adsorbent at 0.5 bar as shown in FIG. 2B. Infact, the composite material 5, which only has 10% adsorbent, exhibitsnearly the same capacity as the pure powder, meaning that much lessactual adsorbent is needed to be utilized in order to achieve similaroxygen uptake capacities under these conditions as shown in FIG. 2A.

The HKUST-1 PVDF films do not have the same enhancement in oxygen uptakeas the electrospun PVDF fibers. The principal difference between thesetwo materials is the phase in which the PVDF polymer exhibits itself.While the HKUST-1 PVDF films are primarily in the γ-phase, theelectrospun PVDF composite is primarily in the β-phase, as confirmedthrough infrared spectroscopy. PVDF exists in five distinct phases, thethree most common are shown in FIG. 3. In the α-phase, the chainconformation alternates trans and gauche for each carbon atom. In theβ-phase, each carbon atom is in the trans configuration. In the γ-phase,a trans-trans-trans-gauche pattern is observed. Of these phases, onlythe β-phase exhibits ferroelectric properties, meaning that the polymeris polarized due to the electronegative fluorine atoms being aligned onone side of the carbon chain, while the more electropositive hydrogenatoms are aligned on the other.

Within the individual crystallites of the β-phase of PVDF, the polymerchains are aligned, creating a localized electric field. Individualpolymer chains are also potentially small enough to penetrate the poresof the MOF. The electric field can extend into the pores of the MOF, orother microporous material, enhancing its adsorption of gases, inparticular, those with otherwise weak attractive forces toward thematerial as shown in FIGS. 4A through 4C.

FIG. 5, with reference to FIGS. 1 through 4C, is a flow diagramillustrating a method of adsorption comprising providing (50) acomposite material 5 comprising a component 10 that creates a localizedelectric field 20 throughout the composite material 5; and a porousmaterial 15 where adsorption occurs, wherein the localized electricfield 20 extends into the porous material 15; and providing (52) anadsorbate 25 for adsorption by the composite material 5, wherein thelocalized electric field 20 created by the component 10 controlsadsorption properties of the porous material 15. The porous material 15the porous materials may be comprised of micro- (less than 2 nm) meso-(2-50 nm) or macro (greater than 50 nm) pores. In one embodiment, theporous material 15 may be microporous. The component 10 may compriseferroelectric material comprising a β-phase of PVDF. The porous material15 may comprise any of zeolites, silicas activated carbons, COFs, PIMs,and MOFs. The MOFs may comprise any of HKUST-1, UiO-66, and UiO-66-NH₂.The method may further comprise electrospinning the β-phase of PVDF andthe HKUST-1 together. The β-phase of PVDF comprises aligned polymerchains, wherein the aligned polymer chains create the localized electricfield 20 extending within the porous material 15. The localized electricfield 20 enhances an adsorption of an adsorbate, a non-polar adsorbate,or oxygen to the porous material 15.

Compared to the conventional adsorption technology of using powders orpellets for adsorption, the composite material 5 enhances theadsorption, specifically for oxygen, significantly, and the compositematerial 5 provides a pliable engineered form to the adsorbate, whichcan more easily be utilized in a device such as gas cylinders, oxygenseparation membranes, and rebreather systems.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of the appendedclaims.

What is claimed is:
 1. A method of adsorption, comprising: providing acomposite adsorbent material comprising a component that creates alocalized electric field throughout said composite material and a porousmaterial where adsorption occurs, wherein said component that creates alocalized electric field comprises ferroelectric material comprising aβ-phase of polyvinylidene fluoride (PVDF) and wherein said localizedelectric field extends into said porous material; and providing anadsorbate for adsorption by said composite adsorbent material, whereinsaid localized electric field created by said component controlsadsorption properties of said porous material.
 2. The method of claim 1,wherein said porous material is microporous.
 3. The method of claim 1,wherein said porous material comprises any of zeolites, silicas,activated carbons, covalent organic frameworks (COFs), polymers ofintrinsic microporosity (PIMs), and metal-organic frameworks (MOFs). 4.The method of claim 3, wherein said MOFs comprise any of HKUST-1,UiO-66, and UiO-66-NH₂.
 5. The method of claim 4, further comprisingelectrospinning said β-phase of PVDF and said HKUST-1 together.
 6. Themethod of claim 1, wherein said β-phase of PVDF comprises alignedpolymer chains.
 7. The method of claim 6, wherein said aligned polymerchains create said localized electric field extending within said porousmaterial.
 8. The method of claim 1, wherein said localized electricfield enhances an adsorption of an adsorbate to said porous material. 9.The method of claim 1, wherein said localized electric field enhances anadsorption of a non-polar adsorbate to said porous material.
 10. Themethod of claim 1, wherein said localized electric field enhances anadsorption of oxygen to said porous material.